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How to replace thermocouple (or thermopile), when burner must be removed

Before spending money, check if pilot is ON

Pilot light is hard to see through sight glass.
Pilot flame is upward from sight glass.
Look into sight glass, and look upward.
Or use mirror to help look through sight glass so you do not have to sit on floor.

Before spending money, push in TCO

Newer models may have TCO located on front of combustion chamber

Lighted inspection mirror
Flame trap inspection mirror at Amazon

Before spending money, get some air

Do NOT underestimate need for adequate air and clean air intake. Save many $ up front right now.
1) Get more fresh air to water heater, especially in very hot location such as attic
2) Clean air intake so combustion can take place

Illustration on left applies to AO Smith, American, State, Reliance, Craftmaster, Kenmore, Whirlpool.
Other brands, and other models, might require removal of combustion parts to access arrestor screen.

Test thermocouple

How to test thermocouple
Test thermocouple and thermopile service manual/ pdf
How to troubleshoot gas water heater
How to install gas water heater

Caution: If you smell gas

Do NOT remove combustion door and expose gas to flame inside water heater

Leave house immediately.
Do not touch light switch on-or-off. Do not touch anything to cause static spark. Do not pick up phone. Call gas company from outside house.
NG natural gas is lighter than air and will rise to nose level, or can gather on ceiling
Propane LP gas is heavier than air and will hug floor.
Do not install LP propane heater below grade (in basement) or gas leak can fill basement will explosive gas.

Water heater safety precautions

Thermocouple or thermopile?

Electronic gas control has thermopile if unit is not pilotless
Thermopile is several thermocouples together, so voltage produced by heat of pilot is large enough to power electonics inside gas control.
Test thermocouple and thermopile/ pdf

Mechanical gas control has thermocouple
Troubleshoot by type of gas control
Thermocouple is 2 different metals with tip sitting in pilot flame. When heat is applied, small current is created that travels to gas contrl valve through copper tube.
If no electric signal is received as gas control valve, then small magnet closes off gas supply.
Thermopile is a cluster of thermocouples. More current is created, and current travels to gas control valve throught small wire. The larger current is enough to power computer chip and error-code indicator light at the gas control valve. If no current is received, the chip closes off gas supply to gas control valve.

Steps start here

Gas water heater burner assembly

Newer models 2009- current (depending on brand and model)

Whole assembly is replaced
Typical 6-year tank has 6 years parts and tank, so the part is covered 6 years, labor covered year 1.
Contact manufacturer with model number, serial number, to find exact part number and warranty coverage.
Water heater manufacturers
Age of water heater

Generic steps for replacing burner parts
Gas water heater burner assembly
Door and burner assembly are removed to replace thermocouple
Larger image

Older models

Gasket may be needed
Generally, water heaters from Rheem, Ruud, Richmond, GE, etc require separate door gasket. Remove carefully if gasket is reused.
Call for parts 1-800-268-6966

Water heaters from AO-Smith, American, State, Reliance, Kenmore, Whirlpool may have one-piece door and gasket that is reusable

Read product manual to identify parts.
If you do not have manual, look at label on side of water heater to identify company     Water heater manufacturers
Burner access door gasket
Some brands require separate door gasket.
Should have gasket on-hand in case removing door causes gasket to tear.
General location of Thermocouple

Note: end of Thermocouple must sit in the pilot flame.
Heat from pilot creates small current that travels to gas control valve, and keeps control valve open so gas will flow to pilot and burner. If thermocouple falls away from pilot flame, or flame goes out, the absence of electric current will turn off gas to pilot and burner.

This type thermocouple requires removal of burner from combustion chamber

Step 1: Turn off gas

Locate gas shut off.
Handle parallel with gas line => Gas ON
Handle perpendicular across gas line => Gas OFF

Rotate gas shut off handle perpendicular across line to shut gas OFF.

Step 2: Notes before starting

Note each tube connected on bottom of gas control.
Note how tight each is when removing, so re-installation is about same.
a) Thermocouple connection is finger tight plus 1/4 turn
b) Manifold tube carries gas to burner
c) Pilot tube carries gas to pilot light
Gas has less psi than water, and connections do not need to be as tight.
Do not overtighten.

These connections do not need pipe sealant or teflon tape.

For propane, manifold tube threads are reverse.
Natural gas, threads are regular.

Step 3: Remove screws

Remove screws holding door

AO-Smith, American, State, Reliance, Kenmore, Whirlpool have hex screw
Rheem, Ruud, Richmond, GE have tamper-proof screws.
Use punch to break out center, and hex to remove

Manifold tab fits into slot, or bracket

DO not dump debris off burner

Step 4: Remove burner

Be careful

Do not dump debris off the burner where it can fall down onto arrestor screen

Burner will hook into a slot, or slide out from under a holder, or slide out of a slot.
Refer to product manual for illustration.
AO Smith-American-State-Reliance-Kenmore-Whirlpool manuals generally have clear instructions and illustrations.
Do not expect Rheem-Ruud-Richmond-GE manual to have illustrations or instructions.

Manifold tab fits into bracket

   Prevent clogging

Step 5: Carfully vacuum out combustion chamber

Keep stuff from falling down onto the air intake screen

Step 6: Get ready to replace

Take photos
Mark-n-measure where new thermocouple should fit
End of Thermocouple must sit in pilot flame 3/8"-1/2" to work correctly
Pilot assembly will be held in location with screws

Step 7: Replace

Remove thermocouple by slowly, firmly pulling and twisting from bracket
If thermocouple will not disengage from pilot assembly, then replace entire assembly

Removal from door might be easier by cutting copper tube with wire cutter
Tip of thermocouple or thermopile is 3/8" to 1/2" into pilot flame
There will be a grommet-type holder to keep thermocouple in place.
Replace thermocouple pdf

If thermocouple will not disengage from pilot assembly, then replace entire assembly

LP and NG models vary

Rule of thumb is .125" [or thickness of nickle]
Igniter and pilot must be positioned closely so gas escaping the pilot orifice will flow into hot ignitor.
Once the pilot ignites, the tip of thermocouple or thermopile must be in the pilot flame.

Image shows 3-legged water heater
This type water heater is easiest to clean without removing combustion parts.

Step 8: Clean the air intake before putting parts back

Rheem, Ruud, Richmond, GE air intake screen located below combustion parts.
AO Smith, American, State, Reliance, Craftmaster, Kenmore, Whirlpool the air instake screen located  bottom of heater.
Use compressed air. Use borescope, or mirror and flashlight to inspect.
Clogged air intake screen will cause overheating.
Move boxes, rags, etc away from water heater for improved air flow
Slow incoming air supply, causes slower venting, yet same amount of gas is burned.
Slow venting with same amount of BTU output will overheat combustion chamber, and trip FV system.
Each manufacturer has different steps for repairing FV overheat, depending on Brand, Age, Model, etc of water heater.

Use soft brush, paint brush, compressed air, vacuum cleaner.

Larger image

Step 9: Re-install burner

Reinstall burner. Wait to reattach door screws until tubes are connected.
Re-connect tubes to gas control valve before attaching combustion door screws.
Manifold tube on LP gas water heater is reverse thread.
Do not overtighten tubes. Remember how tight each connection was when removing.
Thermocouple is finger tight + 1/4 turn.
If thermocouple is overtightened, the electric current produced by thermocouple will short out against gas control valve, and gas control will shut off gas to burner and pilot. Can result in damage to parts and water heater will not function and pilot will not stay lit.

Reinstall combustion door screws, with gasket properly aligned, and sealed

Step 9: Turn on gas

Turn on gas to water heater
Check all connections for gas leak using soapy water.
Use cloride-free soap and water
Propane is heavier than air, so smell close to floor
Natural gas is lighter than air, so smell higher
Give leak time to show itself, since gas pressure is lower than water pressure

Step 10: Light heater

Light gas water heater using instructions printed on side of water heater.
Gas flame should be clear blue, with small amout of yellow and some red.

Step 11: More Options

A) Call service tecnician to fix water heater

B) Continue troubleshooting:
How to troubleshoot gas water heater
How to repair Rheem FVIR

C) Post question on pro water heater forum, and use word search at same site to find previous posts.
Tank forum

D) Install new water heater
How to install gas water heater
Recycle old water heater
Pilot flame troubleshoot Troubleshoot pilot flame
Tip of thermocouple or thermopile is 3/8" to 1/2" into pilot flame

It may be hard to see pilot flame on some models
Sight glass location varies by model of water heater
People often do not get low enough to see pilot flame.
When viewing pilot flame, generally you must look upwards through sight glass and to the right.

Adjust temperature on gas water heater
Troubleshoot gas water heater by type of gas control valve
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